1. Field of the Invention
The present invention relates to an electrophotographic photoconductor (also referred to as xe2x80x9ca photoconductorxe2x80x9d) used in a printer, a copier, or a facsimile machine that employs an electrophotographic process. In particular, the invention relates to a photoconductor that comprises an improved photosensitive material in a photosensitive layer, thereby exhibiting an excellent potential retention rate. The invention also relates to a method for manufacturing such a photoconductor.
2. Description of the Related Art
It is generally known that electrophotographic photoconductors provide the function of maintaining surface charges in the dark, generating charges upon receipt of light, and transporting charges upon receipt of light. Known types of photoconductors include single-layer type photoconductors having all of these functions in a single layer. Also know are laminated-layer type photoconductors consisting of function-separated two layers, where one layer mainly serves to generate charges and another layer serves to maintain surface charges in the dark and to transport charges upon receipt of light.
These types of photoconductors are used for forming images by known electrophotographic methods, such as the Carlson method. Image formation using this method includes the steps of charging the photoconductor by a corona discharge in the dark, forming an electrostatic latent image, such as characters or drawings of an original, on the charged surface of the photoconductor, developing the thus formed electrostatic image by means of toner powder, transferring and fixing the toner powder representing the image onto a support, such as paper.
After the toner transfer, the residual toner powder is removed, and residual charges are erased by light exposure, so that the photoconductor can be used again.
Various substances have been employed as photosensitive materials in electrophotographic photoconductors. For example, inorganic photoconductive substances include selenium, selenium alloys, zinc oxide and cadmium sulfide, dispersed in a resin binder, as well as organic photoconductive substances, such as poly-N-vinylcarbazole, poly(vinyl anthracene), phthalocyanine compound or bisazo compound, dispersed in a resin binder or subjected to vacuum deposition.
Among the organic photosensitive substances described above, the phthalocyanine compound exhibits quite different electrophotographic properties depending its crystal form. A variety of studies have investigated this substance.
Methods for applying the phthalocyanine compounds have been reported not only in cases where one type of that compound is used, but also in cases where two or more types of that compound are used as a mixture.
Uses of two or more types of phthalocyanine compounds by intentional mixing are disclosed in Japanese Unexamined Patent Application Publication (KOKAI) Nos. H2-170166, H2-84661, and H6-145550. Unfortunately, the mixed use of the phthalocyanines in these references was only aiming at a simple use of mixed crystals. No reference discloses a study on difference in positive or negative charge generating ability in a charge generation process of the mixed materials. Xabq
The mixed use of two or more phthalocyanine compounds can be unintentionally conducted by generation of side products during the synthesis process of phthalocyanine. Japanese Unexamined Patent Application Publication (KOKAI) No. H3-35245, discloses discussions on side production of titanyloxo(chlorophthalocyanine) in the synthesis process of titanyloxophthalocyanine. This reference discloses that inclusion of 0.38 to 5 wt % of chlorine is confirmed in the patent documents published in the past. The reference further discloses a detailed study on a synthesis method of titanyloxophthalocyanine that does not generate a side product of chlorine-containing phthalocyanine.
According to the references, titanyloxophthalocyanine with high purity and without lattice defects may be obtained by suppressing generation of the side product of chlorine-containing phthalocyanine. As a result, photoconductors with excellent potential retention capability and high sensitivity may be generated. Unfortunately, the references do not disclose changes in charge generation mechanisms in a case where two types of phthalocyanines are included. The references also do not mention change of potential retention rate depending on the ratio of the contents of the two phthalocyanines in consideration of a charge generation mechanism.
Metal-free phthalocyanines are also studied in terms of various synthesis methods and purification methods, and are disclosed in Japanese Unexamined Patent Application Publication (KOKAI) Nos. H7-2071883 and S60-243089.
These references do not disclose or consider impurities from phthalocyanine derivatives. As a result, no study has been made about variation of charge generation mechanisms due to containment of impurities of phthalocyanine derivatives.
It is known that photoconductors include negative-charging laminated-layer-type photoconductors, positive-charging laminated-layer-type photoconductors, and positive-charging single-layer-type photoconductors.
Synthesis methods of phthalocyanine compound are disclosed in xe2x80x9cPhthalocyaninesxe2x80x9d by C. C. Leznoff et al., 1989, VCH Publishers, Inc. and xe2x80x9cThe phthalocyaninesxe2x80x9d by F. H. Moser et al., 1983, CRC Press, for example. By-production of derivatives in the synthesis process of titanyloxophthalocyanine is disclosed in Japanese Unexamined Patent Application Publication No. H3-35245. A titanylphthalocyanine complex compound may be synthesized by the method disclosed in Japanese Unexamined Patent Application Publication No. H8-302223 or No. H9-230615.
The use of a phthalocyanine compound as a photosensitive material in a photoconductor is known. Methods of synthesis and use of these compound have been studied in some aspects. Unfortunately, a relationship between a charge generation mechanism and a potential retention rate has not been understood or clarified in mixed uses of two or more types of phthalocyanine compounds.
It is an object of the present invention to provide a photoconductor with excellent photoconductive characteristics.
It is another object of the present invention to provide, in particular, an excellent potential retention rates in a photoconductor.
It is another object of the invention to provide a method for manufacturing a photoconductor, the method comprising a step for forming a photosensitive layer with coating liquid and forming a photosensitive layer with an excellent potential retention rate.
Briefly stated, the present invention relates to an electrophotographic photoconductor and manufacturing method. The electrophotographic photoconductor includes a conductive substrate and a photosensitive layer formed on a substrate. The photosensitive layer includes at least a phthalocyanine compound as a charge generation substance. The photosensitive layer contains a first phthalocyanine compound as a main component and a second phthalocyanine compound as a secondary component and as a result, has greater ability to generate negative charges than the ability of the first phthalocyanine compound.
It is to be understood, that to solve the above-described problems, the inventors have made rigorous studies considering the negative-charge-generating ability of the phthalocyanine compound in the charge generation mechanism, and surprisingly found, as a result, that the potential retention rate of a photoconductor significantly increases when second phthalocyanine compound, having higher ability to generate negative charges than that of first phthalocyanine compound, is contained as a secondary component in the photosensitive layer including the first phthalocyanine compound as a charge generation substance.
It is to be further understood, that a potential retention rate of a photoconductor significantly increases when a phthalocyanine compound as a secondary component of charge generation substance is contained in addition to a phthalocyanine compound as a main component of charge generation substance in a coating liquid in the process of manufacturing the photoconductor, where the secondary phthalocyanine compound has higher ability to generate negative charges than an ability of the main phthalocyanine compound.
It is to be understood, that the photosensitive layer in a photoconductor of the invention may be either single layer type or laminated-layer type, and is not be limited to one of the two types. A coating liquid in a method of the invention for manufacturing a photoconductor may be applied to various coating methods including dip-coating and spray-coating, and is not limited to any specific coating method. It is to be understood, that xe2x80x98mmolxe2x80x99 represents xe2x80x98milimole.xe2x80x99
According to an embodiment of the present invention, there is provided an electrophotographic photoconductor, comprising: a conductive substrate; a photosensitive layer on the conductive substrate; the photosensitive layer containing a first phthalocyanine compound as a main component of a charge generation substance and a second phthalocyanine compound as a secondary component of the charge generation substance; and the second phthalocyanine compound having a higher ability to generate negative charges than an ability of the first phthalocyanine compound.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of a central element of the first phthalocyanine compound and a central element of the second phthalocyanine compound is titanium.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of the first phthalocyanine compound and the second phthalocyanine compound is titanyloxophthalocyanine.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of a central element of the first phthalocyanine compound and a central element of the second phthalocyanine compound is gallium.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of a central element of the first phthalocyanine compound and a central element of the second phthalocyanine compound is indium.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of a central element of the first phthalocyanine compound and a central element of the second phthalocyanine compound include hydrogen atoms.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of the first phthalocyanine compound and the second phthalocyanine compound is 29H, 31 H-phthalocyanine.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of the first phthalocyanine compound and the second phthalocyanine compound is X-type metal-free phthalocyanine.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: at least one of the first phthalocyanine compound and the second phthalocyanine compound is X-type metal-free phthalocyanine.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: the second phthalocyanine compound is in an amount of not more than about 600 mmol with respect to of 1 mol of the first phthalocyanine compound.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: the second phthalocyanine compound is in an amount of not more than 600 mmol with respect to of 1 mol of the first phthalocyanine compound.
According to another embodiment of the present invention, there is provided an electrophotographic photoconductor, wherein: the second phthalocyanine compound is contained in an amount of not more than about 200 mmol with respect of 1 mol of the first phthalocyanine compound.
According to another embodiment of the present invention, there is provided a method for manufacturing an electrophotographic photoconductor comprising a step of: forming a photosensitive layer by coating a conductive substrate with a coating liquid including charge generation substance, wherein the coating liquid contains a first phthalocyanine compound as a main component and a second phthalocyanine compound as a secondary component, and the second phthalocyanine compound having a higher ability to generate negative charges than an ability of the first phthalocyanine compound.
According to another embodiment of the present invention, there is provide a method, wherein: an intensity ratio of the second phthalocyanine to the first phthalocyanine in an anion measurement is greater than the intensity ratio in cation measurement in a spectrum of the coating liquid observed by means of laser desorption ionization time-of-flight mass spectroscopy.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.